Array Antennas

An antenna array (or array antenna) is a set of multiple connected antennas which work together as a single antenna, to transmit or receive radio waves. The individual antenna elements are connected to a single receiver or transmitter by feedlines that feed the power to the elements in a specific phase relationship. The radio waves radiated by each individual antenna combine and superpose, adding together (interfering constructively) to enhance the power radiated in desired directions, and cancelling (interfering destructively) to reduce the power radiated in other directions. Similarly, when used for receiving, the separate radio frequency currents from the individual antennas combine in the receiver with the correct phase relationship to enhance signals received from the desired directions and cancel signals from undesired directions.

1. Arrays: Linear, Planar, and Circular By: John Kevin A. Toral

2. Course Outline I) Introduction A) Elements of Antenna B) Gain or directivity of Antenna II) Types of Array A) Linear 1) 2-Element Array 2) N-element Linear Array with Uniform Amplitude and Spacing B) Circular C) Planar

3. Introduction Antenna composes of elements These elements has low values of directivity In application, antennas are required to have very high gains.

4. How to achieve greater gains Increase the electrical size of the antenna Enlarging the dimensions of single elements The most efficient is to use an array.

5. What is an array? An  antenna array is a set of 2 or more antennas. The signals from the antennas are combined or processed in order to achieve improved performance over that of a single antenna. - antenna theory

6. Tasks of Antenna Array Increase the overall gain Provide diversity reception Cancel out interference from a particular set of direction Determine the direction of arrival of the incoming signals To maximize the Signal to Interference Plus Noise Ratio(SINR)

7. Types of Array

8. Linear Arrays Antenna elements arranged along a straight line. Elements of the array are uniformly-spaced.

9. Classifications of Linear Array 2-Element Array N-element Linear Array with Uniform Amplitude and Spacing

10. 2-Element Array

11. The array elements are identical They are oriented in the same way is space (identical polarization) Their excitation is of the same amplitude

12. N-element Linear Array with Uniform Amplitude and Spacing An array of identical elements with identical magnitudes and with a progressive phase is called a uniform array.

13. Circular Array antenna elements arranged around a circular ring. Applications are radio direction finding, air and space navigation, underground propagation, radar, sonar.

14. Unlike linear arrays, circular arrays can provide a 2D angular scan, both horizontal φ and vertical θ scans. Unlike 2D planar arrays, circular arrays are basically 1D linear arrays but in a circular form. Unlike linear arrays, a circular array can scan horizontally for 360° with no distortions near the end-fire directions.

15. Planar arrays Planar arrays are more versatile Antenna elements arranged over some planar surface (example - rectangular array). provide more symmetrical patterns with lower side lobes much higher directivity (narrow main beam). Applications – tracking radars, remote sensing, and communications.